The present invention relates generally to measurement systems, and more particularly, to non-contact measuring of the cut length of moving articles through a manufacturing process. The invention includes an electromagnetic radiation emitter, an electromagnetic radiation receiver, and a measurement processing unit.
Materials undergoing industrial production processes vary widely in physical makeup, such as extruded plastics or steel billets. The speed of movement of these materials as they are being processed also varies widely. Some processes may move a work piece at a very slow rate of speed while other processes may move a work piece at speeds of upwards to 90 mph.
In many manufacturing processes there is an ongoing need to measure the cut length of articles made during a manufacturing process. A wide assortment of devices have been designed to provide precision and repeatability of high speed cut to length operations. In many of these operations, the movement of the uncut article is measured with a pulse counting encoder attached to a driven role or conveyor belt. When the required number of pulses have passed the knife or the saw device, the cutter is triggered and the product is cut to the desired length. In other systems, a through beam photo sensor is broken by the advancing product and the cutter is triggered to cut the product to the target length. Many operating variables may affect the precision of these cut to length systems. For example, the material may slip, stretch or compress on the conveyor belt or driven roller. The cutter may have delays that vary with the thickness or density of the material being cut. The actual mechanical setup may be incorrect in the case of through beam sensors. Also, the sensors may become contaminated and cause unacceptable errors in the finished cut lengths produced.
At present, the accuracy of most cut to length operations must depend on the manual measurement of the finished product by the machine operator or the quality assurance person. Errors can lead to excessive scrap, wasted machine time, or lost orders as the end product is rejected by a demanding customer. The system of the present invention may be used to make accurate, line speed independent, length measurements of moving parts. Depending upon the size of the present system chosen, a wide range of lengths may be measured without physically moving the present invention during the measurement process.
One measurement system which has found substantial acceptance in industry is marketed under the trademark "SCAN-A-LINE.RTM.". The SCAN-A-LINE.RTM. measurement system employs a linear array of electromagnetic radiation emitting diodes positioned on one side of a material, such as a web or sheet moving within a production process. The diodes of the array are illuminated in a scanning sequence having a stable time base, for example, at a 20 KHZ rate developed by a quartz crystal oscillator. Positioned above the moving material under production and opposite the associated diode array, is a tuned photoresponsive receiver which reacts to the illumination emanating from the diodes which are unblocked or partially blocked from view by the receiver by the moving material. Associated controls connected to the receiver are called upon to extrapolate the electromagnetic radiation signals to develop measurement information concerning the material. The extrapolation is based upon the observation that each LED in the emitting array produces a cone of electromagnetic radiation, and the electromagnetic radiation cones from adjacent LEDs overlap in the electromagnetic radiation path to the receiver. The SCAN-A-LINE.RTM. system is marketed by Harris Instrument Corporation of Delaware, Ohio.
The SCAN-A-LINE.RTM. system was first patented in U.S. Pat. No. 5,220,177, which issued on Jun. 15, 1993. The patent described a system wherein each electromagnetic radiation emitting device of the array utilized is energized by a unique drive current which is preselected to cause the emission of electromagnetic radiation exhibiting substantially uniform intensity at the receiver when there is no attenuation of the electromagnetic radiation by a material under edge evaluation.
With the apparatus of the present invention, one or more receivers may be employed with one or more emitters. In the present invention, preferably one receiver is used for each emitter.
The present invention incorporates an array of light emitting diodes to scan a moving part electronically. The light emitting diodes in the array are pulsed sequentially at a predetermined rate. By mathematically processing the time in which light receivers are blocked from receiving the light emitted by specific pulsating light emitting diodes, an accurate length measurement may be made of a moving part in a manufacturing process .